For many uses, for example sensors, integrated optics and the like it is desirable to have planar waveguides available. As shown in FIG. 1a such a waveguide, in its simplest form, includes a waveguide layer 1 with a refractive index nF on a substrate 2 with a refractive index nS and an ambient medium 3, the so-called cover, medium, or cover, with a refractive index nC. The cover medium can in turn be formed by a layer or a layer system, as shown in FIG. 1b. The following applies: nC less than nF and nS less than nF.
For many uses at least one of those layers must be structured. In order for light to be coupled at all into the waveguide, the method which is in fact the most elegant method involves providing the waveguide with a structure 4xe2x80x94a gratingxe2x80x94, as shown in FIG. 2, and coupling the light 5, for example a laser beam, into the waveguide layer 1 by way of diffraction. If the coupling-in angle, grating period and waveguide layer thickness are suitably selected, the light 6 is propagated in the waveguide layer 1 with a given propagation mode and leaves the waveguide for example at an end face 7.
It is immaterial whether the grating 4 is provided at the substrate surface or in or at the waveguide layer.
In addition it is often desirable for the waveguide to be spatially structured as a whole. FIG. 1b shows a waveguide without spatial structuring, FIGS. 3 and 4 show structured strip-type waveguides and FIG. 5 shows a buried strip-type waveguide. FIGS. 6a, 6b, 7a, 7b and 7c are a plan view and a view in section purely by way of example of more complex spatial structurings of a waveguide. Structured waveguides of that kind are widely used for example in the communications art or in the sensor art.
As waveguides of that kind are usually constructed on a glass substrate, the structuring procedures employed are photolithographic methods and the following etching methods: ion milling, reactive ion etching, wet-chemical etching and the like.
Such structuring procedures are time-consuming and expensive.
In addition waveguides on a glass substrate can only be shaped with difficulty and they are sensitive in regard to mechanical stresses such as impact stresses.
The substrate/waveguide layer/environment interaction but in particular the substrate/waveguide layer interaction which is relevant here substantially determines the waveguide property.
The problem of the present invention is to propose a waveguide:
a) in which structuring is substantially simpler and therefore less expensive and which possibly
b) is deformable within limits and/or
c) is less sensitive to mechanical stresses and/or
d) whose substrate can be used flexibly together with different waveguide layers and materials.
This is achieved in a waveguide of the kind set forth in the opening part of this specification.
Particularly when using a polymer, such as for example and as is preferred nowadays a polycarbonate, as the waveguide substrate, it is now very much cheaper to structure the waveguide in particular as a whole, whether this is done by embossing, deep-drawing, injection moulding and the like, and then in particular to provide the coating with a wave-conducting material. In that respect It is found that the application of a wave-conducting material to a substrate of organic material, in particular a polymer, is in no way trivial. It is observed in particular that the losses of a waveguide produced in that way, that is to say waveguide layer directly on the substrate, defined as a drop in terms of intensity with a given mode and a given wave length over a certain distance, are substantially higher, at least by a factor of 10, than when an inorganic material such as for example glass is used as the substrate material.
To our knowledge the problem involved here is substantially new territory. Admittedly there are indications in the literature, for example in xe2x80x9cDesign of integrated optical couplers and interferometers suitable for low-cost mass productionxe2x80x9d, R. E. Kunz and J. S. Gu, ECIO 93-Conferenz in Neuchxc3xa2tel, that integrated optics could be inexpensively made from structured plastics material, but such reports can only document an existing need.
It is self-evident however that on the one hand all structuring procedures for organic materials, in particular polymers, and on the other hand coating processes such as CVD, PECVD, including vapour deposit, sputtering, ion plating, etc., belong to the state of the art. In that respect coating of plastics parts, for example spectacle lenses, reflectors etc. with very different materials also belongs to the state of the art, for example including by means of plasma polymerisation.
Attention should further be directed to the theory of planar waveguides in xe2x80x9cIntegrated Optics: Theory and Technologyxe2x80x9d, R. G. Hunsperger, Springer Series in Optical Sciences, Springer-Verlag 1984.